JPS6356923B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention comprises an optical transmission line having two coupling parts capable of introducing and emitting light, and the light emitted through both coupling parts is superimposed on at least one light receiving surface. The light directed towards one coupling part and the light emitted through this coupling part and directed to the receiving surface cross overlapping paths within a common section in which propagation of multiple modes is possible. It concerns a ring interferometer that travels in the opposite direction.

This type of ring interferometry is a device for determining irreversible transit time differences. When the interferometer is at rest or in constant translation relative to the inertial frame, the propagation of light follows the reciprocity theorem both in the optical transmission path and in the air section, and the optical distance of the light path is two mutually opposite. exactly equal in the direction of propagation. It is also known that all dielectric materials constituting optical transmission lines that are stationary or undergo uniform translation relative to an inertial frame always behave according to the reciprocity theorem in the absence of a magnetic field. When assembling the ring interferometer described above, unexpected irreversible effects may be observed, which may be mistaken for accelerated motion, for example rotational motion.

The aim of the invention is to counteract such unanticipated irreversible effects and the effects of false accelerations or rotations in ring interferometers of the type mentioned at the outset.

The purpose of this is to provide a mode diaphragm in the path where the light sent toward one coupling part of the optical transmission path and the light emitted from this coupling part and guided to the light receiving surface overlap and travel in opposite directions. achieved by.

This invention is based on a new fact discovered by its inventors, namely that the observed irreversibility is reversed in the air section where the light travels once in one direction and then in the opposite direction within the ring interferometer. This is based on the fact that when moving forward, the route taken is somewhat different from the previous section of travel.

Ideally, a mode diaphragm, as its name suggests, allows only one mode to pass through, or in other words, allows only one optical path. However, when light propagates through air, multiple optical paths are possible along the optical axis of the ring interferometer. Therefore, it can be said that higher-order modes can be generated along the optical axis of the ring interferometer in air.

It has been found that the irreversible effect of errors misinterpreted as rotation or other accelerated motion is due to the generation of higher order modes along the optical axis of the interferometer as they propagate through air. This generation of higher-order modes is particularly caused by the fact that the coupling alignment of the single mode optical transmission line is not ideal.

According to the present invention, such higher-order modes are canceled and do not reach the light-receiving surface, thereby eliminating the possibility of being misidentified as rotation or other accelerated motion.

A particularly advantageous embodiment of the invention is the use of a single mode optical transmission line as mode stop. Single-mode optical transmission lines have better properties than the most well-known mode diaphragm, a hole diaphragm plate with extremely small diameter holes, in which only one mode can actually pass through, and no other modes can pass through. present or removed. An advantageous embodiment of a single mode optical transmission line will be described later.

It is effective if the light entering the optical transmission path through one of the coupling parts and the light emitted through this coupling part and guided to the light-receiving surface also pass through the mode diaphragm for this coupling part. It is also advantageous to add another receiving surface, onto which the light emitted from both coupling parts is guided through a further mode diaphragm. Furthermore, the auxiliary light is alternately guided through two mode apertures at the coupling part of the optical transmission path, and the light of one color is guided once through one mode aperture and then through the other mode aperture, or the light of one color is guided through one mode aperture. It is also effective to make light of another color enter through a mode diaphragm and at the same time make light of another color enter through another mode diaphragm, but in this case a problem arises in alignment. That is, the mode diaphragm provided in the optical path of the light sent out from the light source determines the optical axis of the ring interferometer, and the other mode diaphragm must be accurately aligned with respect to this optical axis. If this precise alignment is not performed, the mode aperture will pass one higher order mode and block other modes. This can lead to misunderstandings as irreversible effects.
Although it is difficult in practice to precisely align the different mode apertures with respect to the optical axis of the ring interferometer,
One embodiment of the present invention is constructed so that large errors in the alignment of the mode diaphragm do not have a large effect. In this case the misidentified phase shift is not canceled out, but the true value of the rotational movement can be extracted from it.

The invention will be explained in more detail with reference to the embodiments shown in the drawings.

The ring interferometer shown in FIG. 1 includes a light source 6, for example a laser, from which a laser beam 60 is emitted in the direction of the arrow R. The ring interferometer shown in FIG. A mirror 50 inclined at an angle of, for example, 45 degrees with respect to the R direction is provided in this laser beam to branch a portion of the laser beam toward the light absorbing plate 10.

A light beam 61 that passes through the semi-transparent mirror 50 and is weakened is collected by a condenser lens 33 and focused onto one coupling portion 32 of the single mode optical transmission line 3 . The optical transmission line 3 has a coupling part 31 outside the coupling part 32, and light can be introduced and emitted through both of these coupling parts. This single-mode optical transmission line is advantageously constructed by winding a core-clad glass fiber whose core diameter is at most a few μm. Both end surfaces of this glass fiber become joint parts 31 and 32.

A condenser lens 31 is provided in the optical path of the light beam emitted from the coupling section 31 of the single mode optical transmission line 3.
This lens is arranged so that the point of generation, which is considered to be an ideal light point, of the emitted light beam of the single mode optical transmission line is within one focal plane of this lens.

A parallel light beam 61' is emitted through the lens 30 in a direction R1, which does not necessarily coincide with the direction R, and impinges on the semi-transparent mirror 5, which is placed at an angle of, for example, 45° to the direction R1. This semi-transparent mirror was selected to have 50% transmitted light and 50% reflected light, and a parallel light flux of 6
1' is reflected and branched in the direction perpendicular to R1 as a partial beam 62', and the remaining portion is allowed to pass and proceed in the R1 direction as a partial beam 62.

In the optical path of the partial beams 62 and 62', there are linear polarizers P, P' and quarter-wave plates 21, 21' in the propagation direction.
and condensing lenses 8 and 8' are provided in this order. Linear polarizers P and P' create linearly polarized light, but
In the illustrated position, there is less risk of polarized light returning to its polarized state. The λ/4 plates 21 and 21' convert linearly polarized light into circularly polarized light.

When measurement of rotational motion is carried out based solely on the sanyac effect, in which two lights traveling in opposite directions in a medium create an irreversible travel time difference proportional to the rotational speed when the medium is rotating. In this case, the λ/4 plates 21 and 21' can be omitted. However, if the Faraday effect is used to generate an additional irreversible transit time difference in the optical transmission line for the purpose of canceling the sanyac effect or for other purposes, these λ /4 boards are required. The saniac effect, on the other hand, occurs in all polarization states.

The lens 8 or 8' connects the partial light beam 62 or 62' that has been focused into a parallel light beam to the coupling part 1 of the optical transmission line 1.
1 or 11' to focus. The optical transmission line 1 is also preferably a single mode optical transmission line and is advantageously constructed of a core-clad glass fiber. The diameter of the core of the glass fiber is at most a few micrometers, and both end surfaces are used as joint portions 11 and 11'.

The light introduced into the optical transmission line 1 through the coupling part 11 or 11' travels within the optical transmission line towards the other coupling part 11' or 11, is emitted through these coupling parts, and is reflected by the lens 8' or 8. The light is then focused into a parallel beam of light. This parallel light beam is transmitted through the λ/4 plate 21' or 2
1. After passing through the linear polarizer P' or P, it hits the semi-transparent mirror 5 tilted at 45 degrees. The light emitted through one coupling part 11 of the optical transmission line 1 propagates as a parallel light beam in the opposite direction to the direction R1, and then passes through the other coupling part 1.
The light emitted through R1' propagates as a parallel beam in a direction perpendicular to direction R1. A portion of each parallel light beam passes through the semi-transparent mirror 5 and travels in the same direction as before, but the remaining portion is reflected by the semi-transparent mirror 5 and travels in a direction inclined at 90 degrees with respect to the direction of incidence. This reflected light beam overlaps the transmitted portion of the other parallel light beam and propagates in the same direction.

A parallel light beam in which the light coming from the coupling part 11 and passing through the semi-transparent mirror 5 and the light coming from the coupling part 11' and being reflected by the mirror 5 overlap is shown as 2 in FIG.
A parallel light beam in which the light coming from the coupling part 11 and reflected by the mirror 5 and the light coming from the coupling part 11' and passing through the mirror 5 are superimposed is shown as 2'.

The parallel light beam 2 is superimposed on the parallel light beam 61'.
The parallel light velocity 2 is focused by the lens 30 onto the coupling portion 31 of the single mode optical transmission line 3, and is introduced into the optical transmission line 3 through this coupling portion. The light emitted from the other coupling part 32 of the optical transmission line 3 is focused by the lens 33 to become a parallel beam 20, which hits the semi-transparent mirror 50 at an angle of 45 degrees. A part of the luminous flux 20 travels in the vertical direction as a parallel luminous flux 21 and passes through the condensing lens 34.
corresponds to A known mode diaphragm 35, for example in the form of an aperture diaphragm with a very small diameter aperture, is provided in the focal plane of this condenser lens. This mode aperture 3
5 is used only for the purpose of removing reflected light that is an obstacle.

The light passing through the mode diaphragm 35 hits the photosensitive surface of the detector 40 as the light receiving surface 4. Detector 40 measures the integrated intensity of the incident light and generates an analog signal therefor. Mode aperture 35 may be a single mode optical fiber.

The ring interferometer described above is fully functional on its own and can be used as a rotational motion detector. The effect of being mistaken for rotational motion, which this invention attempts to eliminate, will be explained in detail with reference to FIGS. 3 and 4. These drawings show an enlarged view of one end of an optical fiber 1 having an end face serving as a coupling portion 11. The optical axis of the optical fiber is A, and the lens 8 collects the parallel light beam 62 to focus F on the core K portion of the end face of the fiber 1. The optical axis A' of the parallel light beam 62 is a straight line passing through the focal point F and the center of the lens 8 (here, Gaussian imaging is assumed).

When optical axis A' coincides with optical axis A, the ring interferometer is in ideal alignment. However, in practice, some degree of alignment error is unavoidable, so these optical axes are tilted at a certain angle. This causes the lens 8 to emerge from the end face 11 as shown in FIG.
The optical axis A'' of the parallel light beam focused by the parallel light beam 62 does not exactly coincide with the optical axis A' of the parallel light beam 62, but travels parallel to it.

It is also possible that the optical axis A' of the parallel light beam 62 is offset laterally to the axis A of the optical fiber 1 at the end face 11. In this case, as shown in FIG. 4, the axis A'' of the parallel light beam exiting from the end face 11 and converged by the lens 8 is inclined with respect to the axis of the parallel light beam 62.

The focal point F of the parallel light beam 62 may not be exactly on the end surface 11. In this case, the light emitted from the end face 11 is not turned into a parallel beam by the lens 8, but becomes a diverging beam or a convergent beam.

In the above three cases, for the sake of simplicity, it is assumed that the focal point of the light emitted from the optical transmission line 1, which is an ideal single-mode optical fiber, is on the end face 11.

The above three effects often occur simultaneously. This reduces the coupling efficiency with which the parallel light beam 62 is introduced through the end face of the optical transmission path. However, the result appears as increased damping in the fiber and is not misinterpreted as rotation.

The other coupling part 11', lens 8' and light beam 6
Similar considerations apply to 2'. Luminous flux 6
The position of the light beam 62 of the optical axis 2' relative to the optical axis is determined by the semi-transparent mirror 5. In the example considered here, the optical axis of beam 62' is
perpendicular to the optical axis of

As mentioned before, the light emitted from the coupling 11 or 11' and returning to the light source through the air section passes through a somewhat different optical path than the light when it leaves the light source and is directed to the coupling of the optical transmission line. . This gives a false impression of irreversible effects.

To prevent this phenomenon, the invention proposes to provide a mode stop 3 or 3' in the overlapping optical paths when the light passes through one common section in which propagation of multiple modes is possible.

When the mode diaphragm 3 strongly attenuates higher-order modes, the intermediate coupling part 11 or 1 of the light flux coming from the light source is
1' and a semi-transparent mirror 5 that splits the beam.
Only that part of the light which has passed through a path exactly equal to the optical path length of the light beam introduced through 1 or 11' is received at the receiving surface. In this case, the phenomenon that is mistakenly recognized as an irreversible effect becomes negligible.

In the ring interferometer shown in Figure 1, the parallel beam 2'
It is advantageous to also use the light carried by the for measurement purposes. Therefore, the light receiving surface 4' of the second photodetector 40' is placed in the optical path of this light. The light carried by the beam 2', like the light carried by the beam 2, contains higher order modes which can falsify the measurements due to the three effects mentioned above.

For the above-mentioned reasons, it is effective to provide the light beam 2' with a mode aperture that strongly attenuates higher-order modes. In FIG. 1, for this purpose a single mode optical transmission line 3' with coupling parts 31', 32' is provided for the light beam 2'. The parallel light beam 2' is collected by the lens 30' on the end face of the coupling part 31',
Introduced into optical transmission line. The light emitted from the other coupling portion 32' is focused by the lens 33' to become a parallel beam of light, which impinges on the light receiving surface 4'.

However, this parallel light beam 2' exhibits a behavior that is fundamentally different from that of the parallel light beam on which the parallel light beam 61' is superimposed. If the optical axis of the coupling portion 31' exactly matches the optical axis A' shown in FIG. 3 or 4, good characteristics equivalent to those achieved with the optical transmission line 3 can be obtained. However, since the alignment of these optical axes is not performed with infinite precision, a certain deviation exists between these optical axes, and higher-order modes are introduced into the optical transmission line 3' through the coupling part 31'. For example, the motion may be mistakenly recognized as rotational motion.

If the optical transmission path also transmits higher-order modes, or if this optical transmission path does not exist at all, the phenomenon that is mistakenly recognized as rotational motion becomes significantly greater.

The introduction of a single mode optical transmission line 3 always improves the properties of the ring interferometer, but only when the coupling 31' is properly adjusted can the rotational velocity be measured with high precision by the signal of the detector 40'. can do. Such adjustment is extremely difficult in practice.

On the other hand, since the optical axis A' of the coupling part 31 of the optical transmission line 3 is determined by the position of the coupling part 31, care must be taken that the coupling part 31 of the optical transmission line 3 is always aligned with the optical axis A'. This is due to the fact that the coupling section 31 sends out the light necessary for the operation of the interferometer. The signal of the detector 40 therefore generally allows the rotational speed to be determined with high precision.

FIG. 2 shows an improved version of the ring interferometer of FIG. 1 in which the alignment error of the coupling portion 31' of the optical transmission line 3' does not affect the measurement accuracy. Although this improved type does not eliminate the phase shift that causes misidentification, it does make it possible to determine the true magnitude of the rotational speed.

The main differences between the ring interferometer of FIG. 2 and the embodiment of FIG. 1 are the addition of a light source 6', a semitransparent mirror 50', a lens 34', and a mode stop 35' to cancel harmful reflections. be. In addition to this, a linear polarizer P
1 and P1' and λ/4 plates 22, 23, 22', 2
3' is added in the optical path.

The second light source 6' is a laser like 6.
A laser beam 60' is sent out in the direction R'. A semi-transparent mirror 50' is provided at an angle of 45 degrees to this laser beam, and reflects a portion of it toward the light absorbing plate 10'. The partial light beam 61' that passed through the mirror 50' is
The beam proceeds in the R' direction, passes through the lens 33', focuses on the end face of the coupling portion 32' of the monomode optical transmission line 3', and is introduced into the optical transmission line. This introduced light propagates throughout the ring interferometer in the same way as the light incident on the single mode optical transmission line 3.

The light emitted through the coupling part 32' of the single mode optical transmission line 3' and from which harmful modes have been removed becomes a parallel light beam 2.
0' hits the semi-transparent mirror 50', and the partial beam 21' reflected there hits the additional lens 34'. The focal plane of this lens has an additional mode aperture of 3
5' is provided, and the light passing through this mode aperture impinges on the light receiving surface 4' of the sensor 40'.

When only the light source 6 is used in the ring interferometer shown in FIG. 2, generally higher-order modes are introduced into the optical transmission path 3' through the coupling part 31', so that the signals arriving at the light receiving surface 4' are Rotational motion is generally determined with non-negligible errors.

Next, when the light source 6 is shut off and the light source 6' is turned on in its place, the coupling parts 31' and 31 exchange their roles.
The signal from the light receiving surface 4 of the detector 40 includes an error. However, due to symmetry, this error is opposite to the error included in the signal on the light receiving surface 4'. The error can be canceled by turning on the light sources 6 and 6' alternately and evaluating and combining the signals received by the light receiving surfaces 4' and 4. This combination is, for example, taking an average value.

If the light sources 6 and 6' are made to emit different light, there is no need to turn them on and off alternately. However, in this case, a color filter 14 or 14' is placed in front of the light-receiving surfaces 4, 4', respectively, and the filter 14 allows only the color of the light source 6' to pass through, and the filter 14' only allows the color of the light source 6 to pass through. shall be.
As a result, the light receiving surface 4 receives only the light emitted from the light source 6', and the light receiving surface 4' receives only the light emitted from the light source 6.
In this case, the average value can be taken directly. However, it must be taken into account that the saniac effect used in the case of rotational motion sensors is wavelength-dependent.

In FIG. 2, the λ/4 plate added to the one in FIG. 1 is provided to prevent harmful reflections.

[Brief explanation of the drawing]

FIGS. 1 and 2 are drawings showing conceptual configurations of different embodiments of the present invention, and FIGS. 3 and 4 are enlarged views of parts of these embodiments, respectively. In FIGS. 1 and 2, 6 is a light source, 1 is an optical transmission line having coupling portions 11 and 11', and 3 and 3' are single mode optical transmission lines as mode stops.

Claims (1)

[Claims] 1. One optical transmission line having two coupling parts,
The light emitted from the two coupling parts of this optical transmission path is superimposed and guided to at least one light receiving surface,
The light directed toward one coupling part of the optical transmission line and the light emitted through this coupling part and guided to the receiving surface are mutually connected through overlapping paths in one common section in which propagation of multiple modes is possible. In a ring interferometer that travels in opposite directions, a path in which light traveling toward one coupling part of the optical transmission path and light emitted from this coupling part and guided to the light receiving surface overlap and travel in opposite directions. A ring interferometer characterized by being provided with a mode diaphragm. 2. The ring interferometer according to claim 1, wherein the 2-mode diaphragm comprises a single-mode optical transmission line having two coupling parts through which light can be introduced and emitted. 3. The ring interferometer according to claim 2, wherein the single mode optical transmission line is a core-clad glass fiber, and both end faces thereof constitute a coupling portion. 4. The length of the glass fiber is selected to be such that a clad transmission mode introduced from one end face and proceeding toward the other end face does not reach the other end face. The ring interferometer described in Section 3. 5. The ring interferometer according to claim 3 or 4, characterized in that a device for removing the clad transmission mode is provided. 6. The ring interferometer according to any one of claims 1 to 5, characterized in that a single mode optical transmission line is wound. 7 In addition to the light guided towards one coupling part of the optical transmission line, the light guided towards the other coupling part and the light emitted from this other coupling part and guided to the light receiving surface are also directed to one coupling part. A ring interferometer according to any one of claims 1 to 6, characterized in that the ring interferometer is guided to a light receiving surface through a mode diaphragm.